Sound reflector-modifier for hearing aid microphones

ABSTRACT

A sound reflector-modifier particularly useful to the hard of hearing for improving the quality and clarity of sounds received and reproduced by hearing aids and comprising in combination a sound reflective surface for receiving direct sound waves from a source and for reflecting them into an enlarged end of a sound passage leading to a sound chamber communicating with a sound pickup of a hearing aid.

United States Patent Butts Dvorsky Gorike Beaudry Lehr Thompson Salomonet a1. Hinman Primary Examiner-Kathleen 1-1. Claffy AssistantExaminer-Thomas L. Kundert Attorney-Harris, Kiech, Russell & KernABSTRACT: A sound reflector-modifier particularly useful to the hard ofhearing for improving the quality and clarity of sounds received andreproduced by hearing aids and comprising in combination a soundreflective surface for receiving direct sound waves from a source andfor reflecting them into an enlarged end of a sound passage leading to asound chamber communicating with a sound pickup of a hearing aid.

PATENTED JAN 4 I972 SHEET 2 BF 2 lime/woe SOUND REFLECTOR-MODIFIER FORHEARING AID MICROPHONES he invention relates generally to apparatus forimproving the sound reproduction characteristics of microphones, andmore particularly to a device adaptable for use in combination with ahearing aid to improve the quality and clarity of the sound received andtransmitted by the hearing aid to the auditory nerves.

Persons with impaired hearing have extreme difficulty in comprehendingand distinguishing the diverse sounds around them. Understanding thehuman voice is particularly exasperating, and numerous problems arisewhich are virtually nonexistent for the person with normal hearing.Among these problems are distracting background noise, lack of clarity,poor fidelity, confusing echos and reflections, pitch obscurity,distortion, poor quality, and a general lack of awareness of soundpresence. Various attempts have been made to build hearing aid deviceswhich overcome these problems. Some success has been achieved inobtaining increased amplification and decreased microphone size, but theother problems mentioned above continue to frustrate the partially deafin their quest to achieve and surpass the threshold of soundcomprehension.

Accordingly, it is a primary object of the present invention to providea sound reflector-modifier which helps to overcome the aforementionedsound comprehension problems of the partially deaf.

Another object is to provide a sound reflector-modifier which isadaptable for mounting on the microphone housing of conventional hearingaid devices or alternatively may be manufactured integral with suchhousings.

Still another object of the invention is to provide a soundreflector-modifier which will increase the fidelity and sound clarity ofthe sound waves generated by a human voice and received and developed bya hearing aid device, to enable a person with a hearing deficiency tointelligibly discern and distinguish words generally, and, inparticular, words incorporating the aspirated sounds associated with theletter h, the letters p, t, and k, as well as other letter combinationswhich incorporate the expiratory breath puff in their formation.

A further object is to provide a sound reflector-modifier of theforegoing character including a sound-directing and concentratingpassage between a sound reflective surface and a sound pickup(microphone) of a hearing aid, the reflective surface receiving directsound waves from a sound source and reflecting same into the passage.

Still another object of the invention is to provide a soundreflector-modifier of the foregoing character for use with a hearing aiddevice in which the sounddirecting passage has an enlarged end forpositioning adjacent the human chest to collect and gather sound waveswhich have been reflected from the chest.

A still further object of the invention is to provide a soundreflector-modifier of the foregoing character in which a filteringshield is provided to shield the microphone from harsh direct soundwaves and extraneous sounds so that only sound waves from the reflectivesurface are allowed to pass through the sound passage.

Another object of the invention is to provide a sound reflector-modifierof the character described having a sound chamber in the end of thesound-directing and concentrating passage adjacent the microphone topermit expansion of the sound waves before striking the microphone.

Still another object of the invention is to provide a soundreflectormodifier of the foregoing character with elements in thesounddirecting passage which combine to modify and refine the soundwhich passes therethrough to the microphone.

A further object of the invention is to provide soundreflector-modifiers of the foregoing character having sound-directingpassages of designs which achieve optimum clarity, fidelity, and qualityof sound waves received by microphones of as sociated hearing aiddevices.

A still further object of the invention is to provide a soundreflector-modifier of the foregoing character which is inexpensive, easyto make, and durable, and which may be individually calibrated for theuser.

The foregoing as well as other objects and advantages of the presentinvention may be more clearly understood by reference to the followingdetailed description and accompanying drawings, which togetherillustrate by way of example only various forms of soundreflector-modifiers for microphones embodying the present invention.

In the drawings:

FIG. I is a perspective view of one: form of the invention showing aperson using a conventional hearing aid device with a soundreflector-modifier mounted on the microphone and amplifier housingthereof;

FIG. 2 is a front view of the modifier of FIG. 1 with a portion cutaway;

FIG. 3 is a sectional view of the modifier of FIG. 1 taken along line3-3 of FIG. 2;

FIG. 4 is a perspective view of-the modifier of FIG. 1 shown from athreequarter front position;

FIG. 5 is an alternate form of the modifier of FIG. 1 shown from thesame view as FIG. 4;

FIG. 6 is a front view of another form of a sound reflectormodifiermounted on a housing for a microphone of a hearing aid device;

FIG. 7 is a side sectional view of embodiment of FIG. 6 taken along line7-7; and

FIG. 8 is another embodiment of the modifier mounted on a hearing aidmicrophone housing having a sound-receiving aperture on a face thereof.

As previously indicated, my sound reflector-modifier is particularlyuseful in combination with conventional hearing aid devices. Inparticular, when so combined, it has proven under actual test conditionswith those of impaired hearing to dramatically reduce the effects ofbackground noise which has heretofore cluttered and distracted from andsometimes precluded detection of desired sound waves. Moreover, my soundreflector-modifier when employed in conjunction with a conventionalhearing aid device has proven in such instances to materially improvethe clarity and fidelity of the sound waves reproduced by the hearingaid device and received by the listener. In short, whereas when thepartially deaf utilize conventional hearing aid appliances they areunable to clearly distinguish the pitch of various tones, are confusedby echoes and reflections and background noise and are unable todistinguish certain breath tones; when my modifier is added to suchhearing aid devices they are immediately able to clearly distinguish andrecognize such tones and on actual tests have reported to me substantialelimination of problems produced by background noise, echoes,reflections, and distortions.

Generally speaking, my sound reflector-modifier includes an ear memberin combination with a sound reflective surface. In the drawings, themodifier, ear member, and reflective surface are designated by thenumerals 10g 12, and 14 respective' ly.

When the sound reflector-modifier 10 is utilized with a hearing aiddevice, as for example in FIG. 1, the ear member 12 is mounted on themicrophone housing 16 of the device to face the sound reflective surface14 (here the chest of the listener) and to communicate with themicrophone in the housing through an aperture 18 (see FIG. 2). Soundwaves from a source strike the sound reflective surface 14 and reboundinto the ear member 12 where they are concentrated, directed, andmodified as they travel through a sound passage 20 in the ear member tothe microphone. At the microphone and in circuitry of an amplifiercircuit associated therewith, the sound waves are converted intoelectrical signals, amplified and transmitted by an electrical lead 22to an earpiece 24 (speaker) in the ear of the listener. In the earpiece24 the electrical signals are reconverted into sound waves which actupon the auditory nerves in the ear and head of the listener to producethe sensation of sound.

It bears emphasizing that my invention utilizes sound waves reflectedfrom a sound reflective surface into a sound passageway leading to themicrophone of the hearing aid device. This is to be distinguished fromhearing aid appliances which collect direct sound waves from a soundsource. In my invention, 1 have found through testing of various hearingaid devices with various persons having impaired hearing that thecombination of my invention including the sound reflective surface 14and the sound directing and concentrating passage designed such thatonly reflected waves are received at the microphone, has the unexpectedresult of materially improving the clarity and fidelity of the soundwaves reproduced by the hearing aid device and transmitted to the ear ofthe partially deaf listener while substantially reducing the distractingeffects of background noise, overcoming pitch obscurity, the effects ofdistortion, and possibly of most importance allowing the listener toclearly distinguish vocal sounds which he or she has heretofore not beenable to distinguish such as sounds associated with letters h, p, t, andk.

The exact manner in which my invention operates upon the sound waves asthey strike the sound reflective surface and are gathered, directed, andmodified in the sound passage leading to the microphone is not fullyunderstood. However, from my practical tests, it appears that the use ofthe sound reflective surface together with my sound passage,substantially eliminates, at least as far as the listener is concerned,sound waves which are out of phase with each other reaching themicrophone, preclude background noise from reaching the microphone withsufficient volume to have any noticeable effect upon the desired soundwaves transmitted to the ear of the listener. Moreover, throughgathering, reflection, concentration, and expansion of the sound wavesin the sound passage, my invention improves the clarity and fidelity ofthe desired sound waves received by the microphone and reproduced by thehearing aid device to enable the partially deaf listener to achieve andsurpass his or her threshold of sound comprehension in a mannerheretofore unattainable with known hearing aid applicances. Since I amnot certain as to the exact mode of operation of my invention andexactly how it achieves the indicated results, the explanation offeredherein as to the inner operation of my invention upon the sound wavesshould not be considered as limiting upon my invention but simply asbeing the way in which my invention appears to me to operate and producethe desired results.

Referring now more particularly to the preferred embodiment of myinvention illustrated in FIGS. 2, 3, and 4, the ear member 12 extendsvertically from a basemember 26 and includes upper and lower portions 28and defining the sound passageway 20. The base 26 is generallyrectangular, includes openings for receiving control dials for thehearing aid circuitry, and is designed to fit tightly over a top of thehousing 16 including the aperture 18. Additional sealing means, such asan adhesive, may be incorporated to secure the ear member to the housingif desired or, alternatively, the ear member 12 may be formed integralwith the housing 16 over the aperture. In either case, the soundpassageway 20 communicates directly with the aperture 18 and themicrophone within the housing.

In the illustrated form, the ear member 12 resembles a folded funnel. Inthis regard, the lower portion 30 of the ear member 12 extends above thebase 26 at an angle toward the reflective surface 14. The upper portion28 of the ear member 12 extends upwardly and forwardly from the lowerportion 30 such that an upper lip 32 thereof contacts the soundreflective surface 14, which in the exemplary form is the listenerschest, with the central axis of the upper portion substantiallyperpendicular to the reflective surface and to the central axis of thelower portion.

In my experimentation, the shape and location of the open ing 31 of thepassage 20 adjacent and facing the reflective surface I4 has been foundto be of particular importance in improving the quality of the soundpassing to the microphone and reproduced by the hearing aid device. Inthis regard, it has been found highly desirable to limit the sound wavesentering the passageway 20 to those that rebound from the reflectivesurface 14. In the illustrated form, this object is achieved by shapingthe opening 31 in the form of an enlarged rectangle, the edges of therectangular opening being determined by the upper lip 32 which extendsoutward beyond an abbreviated lower lip 34. The upper lip 32 actuallycontacts the reflective surface 14 while the lower lip 34 is spacedtherefrom. As illustrated in FIG. 3, such an arrangement of the upperand lower portion of the ear member 12 in combination with this soundreflective surface 14 defines a chasm therebetween. The chasm permitssound waves rebounding from the surface to be reflected into andgathered by the enlarged open end 31 of the passageway 20 and inpractice appear to effectively limit the waves entering the passagewayto such reflected waves. While such a rectangular-shape opening ispreferred for the opening 31, the opening may take other forms so longas they permit the upper portion 28 to act as a shield in filtering allthe direct waves and most of the undesired indirect and extraneous soundwaves from traveling into the passage 20.

The configuration of passage 20 between the opening 31 and an opening 35at the base of the lower portion 30 communicating with the aperture 18is also particularly important in assuring that sound waves of thepreferred quality are received by the microphone within the housing 16.A preferred shape for the passage 20 is shown in FIGS. 2, 3, and 4 asbeing a modified hourglass shape. With the hourglass-shaped passage 20,sound waves rebounding from the reflective surface 14 are gatheredthrough the opening 31 and directed by the upper funnel-shaped portionof the passage toward an intermediate portion 36 of relatively smallcross-sectional area. The sound waves in entering the intermediateportion 36 are reflected and rebound from and between the sides of thepassageway and are concentrated. From the intermediate portion 36, theconcentrated sound waves enter the lower portion of the passageway 20where they are allowed to expand prior to passage through the aperture18. In this regard, the lower portion of the passageway 20 below theintermediate portion acts as a sound chamber. Dimensionally, the soundchamber has a shorter axial length and a smaller cross-sectional areathan the upper portion of the hourglass passage adjacent the surface 14.In addition, the axes of the two openings of the hourglass passage 20are displaced approximately from each other.

While the invention is not limited to the specific dimensions and shapeof the sound passage 20 just described and illustrated, the quality,clarity, timbre, and pitch have been improved the most by employing asound passage 20 having an enlarged end defined by the upper portion 28which connects through a constricted intermediate portion 36 forfocusing and concentrating the sound, to a sound chamber defined by thelower portion 30, which sound chamber communicates with the microphonethrough the aperture 18.

Sometimes the configuration of the passage 20 is determined in part bythe location of the aperture 18 in the housing 16. For example, theembodiment shown in FIG. 8 includes an aperture 18 in a front face ofthe housing 16. In that case, the ear member 12a is located on the frontof the housing and defines a more conventional hourglass-shaped passage20a with its axis inclined slightly upward. Similar adaptations of theear member and sound passage therein may be made to facilitate use ofthe invention with microphones having variously sized apertures invarious positions on the housing without diminishing the salutaryacoustical results.

It will be appreciated that the quality of sound received and reproducedby the hearing aid device is affected by many factors as the wavesrebound from the reflective surface 14 through the passage 20 and theaperture I8 to the microphone. I have discussed above the importance ofthe shape and size of the passage opening adjacent the reflectivesurface 14, as well as the spatial relationship of the upper and lowerlips 32 and 34 with the reflective surface 14. The importance of thesound-directing passage configuration has also been discussed, includingthe structural details of the preferred passage 20 having a modifiedhourglass shape. A further factor affecting the quality of the sound isthe aperture 18. As shown in the drawings, a conventional filter membersuch as a grille 33 is attached to the housing and completely fills theaperture opening. It has been determined by experimentation that thegrille 38 only partly performed its task of filtering and dampingextraneous and strident elements of the sound passing through theaperture to the microphone. Accordingly, in a preferred form of myinvention a perforated tape 40 made, for example, from plastic and/oraluminum foil may be suitably attached under the lower portion 30 of theear member 12 to completely cover the grille 38. In practice subtle finetuning has been obtained by varying the size, number, and location ofthe perforations in the tape 40. For example, and as shown in FIG. 5,the quality of sound passing through the aperture 18 and grille 3b tothe microphone was improved in some instances by placing a tape 40having a single circular perforation in the center thereof over thegrille and by using an ear member llZb in which the lower portion 30band the upper portion 23b define a funnellike passage 20b having itssmall opening positioned to communicate through the circular perforationto the aperture 118, with the large opening of the large funnellikepassage being designed, as before, for location in the vicinity of andsubstantially facing the reflecting surface 14. The shape and positionof the upper and lower lips 32b and 34b are similar to that of thepreferred embodiment discussed above, such that the axes at the oppositeends of the funnellike passage are substantially normal to each other.

Referring to FIGS. 6 and 7, it was found experimentally that byproviding a modified configuration for the ear member 12c, and byinterposing various additional elements in the modified sound-directingpassage 20c, it was possible to introduce additional factors which wouldaffect the quality of the sound being transmitted through the aperture118 to the microphone. More particularly, the lower portion 30c of theear member 12c in the embodiment includes a first rectangular box 42with its back and sides secured as by adhesive and extending from thecorresponding back and sides of the housing 16. The upper end of the boxmember 42 is closed by a panel 44 respectively perpendicular to the backand sides thereof and extending across and within the passage 200. Theopen side of the reflector box 42 faces the reflective surface 114 forreception, concentration, and reflection of sound waves coming from thereflective surface. Two sound focusing and filtering louver members 46are disposed in parallel position across the reflector box 42 just belowthe panel 44 with the front edges being inclined slightly upward todirect sound toward the aperture. An inner member or cap 4% having aspherical quadrant shape is located in the reflector box 42 below thelouvers and is designed to be fitted around the aperture 18 with itsopening facing toward the reflective surface 14. The cap 48 functions tocollect and concentrate the sound waves and to direct them through theaperture 1%. The size, shapes, and positions of the louvers and capwithin the part of the passage 20c defined by the lower portion 34% maybe varied in order to achieve the optimum clarity and fidelity for theindividual user.

In he embodiment of FIGS. 6 and 7, it was found helpful to cover with afilter cloth 50 the subchambers formed by the reflector box 42, louvers46, and the cap 48. The filter cloth 50 serves to temper the glare ofthe sound waves as they bounce off the reflective surface 14 and arereflected and modified in the passage 20c on their way toward theaperture 18.

In the embodiment of FIGS. 6 and 7, the upper portion 28c of the earmember 120 is located directly above the lower portion 30c and includesa second box reflector 52 wider than the first reflector box 42 with itssides 54 and top 56 depending outwardly for gathering and concentratingthe sound waves rebounding from the reflective surface 14.

Since in the embodiment of FIGS. 6 and 7, the ear member does not extendbeyond the front face of the housing 16 (in contrast with the otherembodiments), it is necessary to pro vide a protruding support on thefront face of the housing such as a spacer block 5% to produce thedesired sound chasm outside the sound passageway Zflc to capture wavesrebounding from the surface 14. Thus as illustrated in FIG. 7 with theblock 5%, the top 60 of the upper portion 280 and the block contact thereflective surface 14, define the chasm and thereby produce sufficientclearance between the passage 20c and the surface I4 for gathering thosesound waves rebounding from the surface.

It will be appreciated from the foregoing that my invention modifies,concentrates, filters, dampens, and refines the sound waves passingthrough the passage 20 and the aperture 18 to the microphone to producesound of increased fidelity and improved clarity and quality. Inaddition, the ear member 12 may include a sound passage of variousoptimum configurations as determined experimentally wherein elements ofdif ferent sizes and shapes are chosen and positioned to optimize theacoustical characteristics of the device for the individual user.

Moreover, although my invention has been described in combination with ahousing in a hearing aid device suspended over the chest ofa listener,its use is not to be limited to such a setting or such a combination. Infact, my invention including the ear member and sound reflective surfacemay be usefully employed wherever it is desired to modify soundreception of a microphone and the sound reproduced by associatedcircuitry and speaker systems.

Furthermore, while preferred embodiments of my invention have beendescribed in some detail herein, changes and modifications may be madein the illustrated forms without departing from the spirit of myinvention. It is therefore intended that my invention be limited inscope only by the terms of the following claims.

I claim:

1. A hollow generally ear-shaped sound reflector-modifier for capturingonly reflected sound waves rebounding from an immediately adjacent soundreflective surface and for directing the captured reflected sound wavesto a hearing aid microphone enclosed in a case in a manner whichincreases the fidelity and clarity of the sound waves, comprising:

a first housing portion including outwardly and forwardly dependingsides facing said sound reflective surface, an upper edge directedtoward said sound reflective surface with a forward upper lipimmediately adjacent thereto, a front face below said upper edge facingsaid sound reflective surface and relieved below said upper lip awayfrom said sound reflective surface, and a back face rearward of saidfront face for shielding said front face from direct sound waves from asource rearward of said back face whereby said front face combines withsaid sound reflective surface to form a chasm for capturing onlyreflective surface;

a second housing portion extending from said first housing portion;

means for mounting said second housing portion on said case over anaperture open to said microphone such that the microphone is shieldedfrom said direct sound waves from said source; and

sound passageway means for directing the captured reflected sound wavesfrom said chasm to said microphone while increasing the fidelity andclarity of said reflected sound waves, said passageway means having afirst open end in said front face immediately below said upper lip andcomprising substantially the entire area of said front face forreceiving sound waves rebounding from said sound reflective surface, asecond open end in said second portion over said aperture open to saidmicrophone, and means defining a substantially spherical quadrant-shapedmember in said second portion including said second open end and anopening to said sound reflective surface.

2. The sound reflector-modifier of claim I further including in saidsecond housing portion sound wave deflecting louvers inclined relativeto the direction of reflected sound waves rebounding from said soundreflective surface into said chasm for directing said reflected soundwaves toward said aperture.

3. A hollow generally ear-shaped sound reflector-modifier for increasingthe fidelity and clarity of sound waves received by a hearing aidmicrophone housed in a case supported against the chest of its wearer,comprising:

a lower housing adapted for mounting on said case over an apertureleading to said microphone to shield said microphone from direct soundwaves;

an upper housing extending upward from and forward of said lower housingtoward said chest and including an upper edge having a forward upper lipengaging said chest, a front face below said upper edge facing saidchest and relieved below said upper lip away from said chest, and a backface rearward of said front face for shielding said front face fromdirect sound waves from a source rearward of said back face whereby saidfront face combines with said chest to form a chasm for capturing onlyreflected sound waves rebounding from said chest; and

a passageway through said upper and lower housings for directing thecaptured reflected sound waves from said chasm to said microphone whileincreasing the fidelity and clarity of said reflected sound waves, saidpassageway having a first open end in said front face immediately belowsaid upper lip and comprising substantially the entire area of saidfront face for receiving sound waves rebounding from said chest, asecond open end axially displaced about from said first open end andbeing in said lower housing over said aperture in said case, an axiallyelongated funnel-shaped upper passage portion including said first openend and extending therefrom rearwardly and downwardly to an intermediatepassage portion of relatively small cross-sectional area, and a lowerpassage portion extending from said intermediate passage portion in saidlower housing and including said second open end and having a shorteraxial length and a smaller cross-sectional area than said upper passageportion.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. R5,632,902 I .Iannary L, l212 lnvent fl JOHN J WAHLER It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 6 line 51, after "only" insert "reflected sound waves reboundingfrom said sound Signed and sealed this 6th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETC.HER,JR. ROBERT GOTTSCHALK Attesting Officer ICommissioner of Patents FORM P040550 1 uscoMM-Dc 60376-P69 US.GOVERNMENT PRINTING OFFICE 1 I969 0-366-334

1. A hoLlow generally ear-shaped sound reflector-modifier for capturingonly reflected sound waves rebounding from an immediately adjacent soundreflective surface and for directing the captured reflected sound wavesto a hearing aid microphone enclosed in a case in a manner whichincreases the fidelity and clarity of the sound waves, comprising: afirst housing portion including outwardly and forwardly depending sidesfacing said sound reflective surface, an upper edge directed toward saidsound reflective surface with a forward upper lip immediately adjacentthereto, a front face below said upper edge facing said sound reflectivesurface and relieved below said upper lip away from said soundreflective surface, and a back face rearward of said front face forshielding said front face from direct sound waves from a source rearwardof said back face whereby said front face combines with said soundreflective surface to form a chasm for capturing only reflected soundwaves rebounding from said sound reflective surface; a second housingportion extending from said first housing portion; means for mountingsaid second housing portion on said case over an aperture open to saidmicrophone such that the microphone is shielded from said direct soundwaves from said source; and sound passageway means for directing thecaptured reflected sound waves from said chasm to said microphone whileincreasing the fidelity and clarity of said reflected sound waves, saidpassageway means having a first open end in said front face immediatelybelow said upper lip and comprising substantially the entire area ofsaid front face for receiving sound waves rebounding from said soundreflective surface, a second open end in said second portion over saidaperture open to said microphone, and means defining a substantiallyspherical quadrant-shaped member in said second portion including saidsecond open end and an opening to said sound reflective surface.
 2. Thesound reflector-modifier of claim 1 further including in said secondhousing portion sound wave deflecting louvers inclined relative to thedirection of reflected sound waves rebounding from said sound reflectivesurface into said chasm for directing said reflected sound waves towardsaid aperture.
 3. A hollow generally ear-shaped sound reflector-modifierfor increasing the fidelity and clarity of sound waves received by ahearing aid microphone housed in a case supported against the chest ofits wearer, comprising: a lower housing adapted for mounting on saidcase over an aperture leading to said microphone to shield saidmicrophone from direct sound waves; an upper housing extending upwardfrom and forward of said lower housing toward said chest and includingan upper edge having a forward upper lip engaging said chest, a frontface below said upper edge facing said chest and relieved below saidupper lip away from said chest, and a back face rearward of said frontface for shielding said front face from direct sound waves from a sourcerearward of said back face whereby said front face combines with saidchest to form a chasm for capturing only reflected sound wavesrebounding from said chest; and a passageway through said upper andlower housings for directing the captured reflected sound waves fromsaid chasm to said microphone while increasing the fidelity and clarityof said reflected sound waves, said passageway having a first open endin said front face immediately below said upper lip and comprisingsubstantially the entire area of said front face for receiving soundwaves rebounding from said chest, a second open end axially displacedabout 90* from said first open end and being in said lower housing oversaid aperture in said case, an axially elongated funnel-shaped upperpassage portion including said first open end and extending therefromrearwardly and downwardly to an intermediate passage portion ofrelatively small cross-sectional area, and a lower passage portionextending from said intermediate passage portion in said lower housingand including said second open end and having a shorter axial length anda smaller cross-sectional area than said upper passage portion.